1. Field of the Invention
The present invention relates to a magnetooptical recording magnetic head and a magnetooptical recording apparatus for recording information signals in a magnetooptical recording medium in accordance with a magnetic field modulating scheme.
2. Related Background Art
A magnetooptical recording apparatus using a magnetic field modulating scheme is known as a magnetooptical recording apparatus for recording information in a magnetooptical recording medium, such as a magnetooptical disk, at a high density. In this scheme, laser light converged into a light spot about 1 .mu.m in diameter is irradiated onto a recording medium, and a magnetic head applies a magnetic field modulated by an information signal onto a portion irradiated with the laser light, thereby recording the information signal.
A generally known magnetooptical recording apparatus of the magnetic field modulating type has an arrangement as shown in FIG. 1. A magnetooptical recording medium 1 used in this apparatus is a disk-like medium manufactured by forming a signal recording layer on a transparent substrate. The disk 1 is rotated by a spindle motor 2. During this rotation, a floating magnetic head 3 is located on the upper surface side of the disk 1, and an optical head 4 is located on the lower surface side of the disk 1 at a position opposite to the floating magnetic head 3. The magnetic head 3 is held at the distal end of a suspension 5, and the fixed ends of the optical head 4 and the suspension 5 are connected to each other by a connecting member 6, thereby constituting a magnetooptical unit. The connecting member 6 is mounted on a linear motor 7. The optical head 4 and the magnetic head 3 are therefore driven by the linear motor 7 to together move in the radial direction of the disk 1.
To record an information signal on the disk 1 in the above magnetooptical recording apparatus of the magnetic field modulating type, the optical head 4 irradiates laser light 8 onto the signal recording layer of the disk 1 while the disk 1 is rotated at a high speed by the spindle motor 2, thereby forming an image of the laser light as a light spot about 1 .mu.m in diameter on the signal recording layer. This consequently increases the temperature of the signal recording layer up to the Curie temperature or more. At the same time, the magnetic head 3 is driven by a magnetic head driving means 9 to apply a bias magnetic field modulated in accordance with the information signal to the portion whose temperature is raised. As a result, the direction of magnetization of the signal recording layer is pointed in the direction of the bias magnetic field to thereby record the information signal on the signal recording layer.
The arrangement of the magnetooptical recording magnetic head 3 used in the above magnetooptical recording apparatus is shown in FIGS. 2A and 2B. FIG. 2B is a perspective view showing the overall magnetic head, and FIG. 2A is an enlarged view showing a core of the magnetic head. This core C is generally made of ferrite with a high permeability. A coil W is wound around the main magnetic pole of the core C. The magnetic head moves while floating with a small gap kept with respect to the disk by means of an air stream produced by the high-speed rotation of the disk. The magnetic head, therefore, has a slider SL with an aerodynamic floating surface. The slider SL consists of a nonmagnetic material, such as ceramic. The core C and the slider SL are fused to each other via glass G.
FIG. 3 is a graph showing the relationship between the recording current flowing through a coil of a conventional magnetooptical recording magnetic head and the generating magnetic field of the magnetic head. FIG. 3 shows an example of conventional, standard magnetic heads in which a core consists of ferrite with a saturation magnetic flux density of 5 kG, the dimensions of a magnetic pole are 0.15 mm.times.0.15 mm, and the number of turns of a coil is 20. Generally, it is necessary to apply a bias magnetic field of 200 to 300 Oe in order to perform signal recording on a magnetooptical disk in a good condition. The graph shown in FIG. 3 demonstrates that the generating magnetic field is proportional to the recording current when the recording current is small, and is saturated with an increase in the recording current. This is so because the magnetic flux density inside the core cannot increase beyond the saturation magnetic flux density of ferrite.
In addition, the magnitude of the saturation magnetic field depends on the frequency f of the recording signal as shown in FIG. 3; the higher the frequency f, the lower the saturation magnetic field. Such a phenomenon is caused because a high-frequency loss (which is primarily a property inherent in the magnetic material forming the core) of the magnetic head increases to cause the magnetic head to generate heat as the frequency f of the recording signal rises, and the saturation magnetic flux density of ferrite forming the core decreases accordingly. As an example, FIG. 4 shows the temperature dependency of a saturation magnetic flux density Bs of ferrite used in a core of a conventional magnetooptical recording magnetic head. As shown in FIG. 4, although the saturation magnetic flux density Bs of ferrite is 5 kG at room temperature (25.degree. C.), it decreases with an increase in temperature and becomes approximately 3 kG at 100.degree. C.
A strong demand has recently arisen for higher-speed signal recording in such a magnetooptical recording apparatus, and so it becomes necessary to raise the frequency of a recording signal accordingly. If the frequency of a recording signal is raised as described above, however, the saturation magnetic field is lowered by an increase in the high-frequency loss of the magnetic head. For example, if the frequency of a recording signal is increased up to 10 MHz or more as shown in FIG. 3, it is impossible to obtain a generating magnetic field of 200 Oe or more which is required to perform signal recording in a good condition even at the maximum recording current. As described above, higher-speed signal recording is impossible because the frequency of a recording signal is limited by the performance of the magnetic head.